In many endodontic operations, it is necessary to successively insert an elongated instrument into, and then pull the same from, the root canal of a tooth in order to thoroughly remove any inflamed or necrotic tissue therein and properly enlarge the canal. The instrumented root canal is subsequently sealed off with aseptic material.
As shown in FIG. 1, the conventional endodontic instrument 10, which is used in the root canal treatment described above, generally consists of a thin, flexible wire 12, with an abrasive surface acting as a file, a reamer, or the like, a handle 16 and a rubber stop 14. The handle 16, which is adapted for gripping by the operator, is securely affixed at one end of the wire 12. The rubber stop 14, on the other hand, is movably attached to the wire 12 and can be easily relocated therealong.
The position of the stop 1 at the wire 12 determines the working length 18 of the instrument 10, i.e., the length of the wire 12 to be embedded in the tooth during the treatment, since the stop 14 prevents further penetration of the wire 12 into the canal in the tooth when its bottom surface bumps onto the incisal edge or cusp tip of the tooth being treated.
There are several drawbacks associated with the conventional instrument. For example, the stop 14 may slip without being noticed by the operator during the treatment, thereby causing over-instrumentation or under-instrumentation of the canal.
Also, while the working length 18 is usually determined by radiography, adjustment of the position of the stop 14 by relocating it along the wire 12 is usually required. Thus, the stop 14 may be incorrectly positioned by the operator because of his or her biases or inexperience.
Similarly, when preparing a series of endodontic instruments of various diameters to be used in treating the same canal, there may be discrepancies of the working lengths among the instruments because of the operator's biases or inexperience. This greatly increases the possibility of incomplete instrumentation or even perforation of the canal.